1. Field of Invention
The invention relates to a hybrid drive system which drives a vehicle using an internal engine and a motor/generator. More specifically, it relates to a hybrid drive system using an infinitely variable transmission (IVT).
2. Description of Related Art
A conventional hybrid drive system using a continuously variable transmission (CVT) is proposed as described in Japanese Patent Publication Laying-Open No. 9-71138. In this system, an engine and a motor/generator are directly connected to each other via a damper. Further, the output shafts of the engine and the motor/generator are connected to an oil pump and the CVT via a forward-reverse change mechanism having a forward clutch and a reverse brake, and further connected to vehicle wheels via gears and so on.
When the vehicle is stopped at, for example, an intersection, the engine is stopped in order to improve fuel consumption, and engine surging or reviving is prevented by performing a regenerative control to the motor/generator.
In the aforementioned conventional system, the motor/generator is operated as a motor (starter-motor) at the engine start, and after engine is started, the vehicle is moved by engaging, for example, the forward clutch after waiting for an increase in the hydraulic pressure created by the oil pump.
Therefore, the vehicle can not be moved by the motor/generator when the engine is stopped. As a result, it is difficult to improve the fuel consumption and to reduce the exhaust gases in, for example, a town area in which the vehicle is started and stopped repeatedly.
The vehicle is slow to start moving at the restart because the engagement of the forward clutch and a shift operation of the CVT are performed after the hydraulic pressure is increased according to the rotation of the oil pump which is operated by the engine.
When the engine is stopped during a vehicle stop, the auxiliary equipment can not be operated. Even if an electric motor, separate from the described driving system, such as a motor/generator arranged to drive the auxiliary equipment and the oil pump is provided, another driving system is needed, the vehicle cost is increased, and the system becomes complicated.
Further, even if vehicle movement by the motor/generator, without using the engine, is made possible by interposing a clutch between the engine and the motor/generator, when the clutch is disengaged, the oil pump and the auxiliary equipment can not be operated. Therefore, as discussed, another drive system is needed. Further, the clutch is needed to perform slip control at the start of vehicle movement because the CVT can not shift from rotation 0. Such a system is more complicated. Further, the reliability of the hybrid driving system is decreased, based on the durability of the clutch, due to the slip.